1. Field of the Invention
The present invention relates to a glue applicator which is mounted in a gluing machine just before a double facer in a corrugating machine and which is for the supply of glue to corrugation flute tips of a single-faced currugated board.
2. Description of the Related Art
A schematic construction of a gluing machine portion mounted in a corrugating machine will now be described with reference to FIG. 8. A conventional glue applicator mounted to a gluing machine 1 in a corrugating machine comprises a glue supply portion 5 and a rider roll 6. The glue supply portion 5 comprises a glue applicator roll 2, a doctor roll 3 and a glue reservoir 4 located below the glue applicator roll 2. The rider roll 6 is opposed to the glue applicator roll 2 through a predetermined clearance. By the glue applicator, glue 9 is transferred and supplied to flute tips of a core board 8 of a single-faced corrugated board 7 which travels between the glue applicator roll 2 and the rider roll 6.
On the board inlet side of the glue applicator roll 2 is disposed a presser roll 10, while on the board discharge side of the roll 2 is disposed a tension roll 11. By means of the presser roll 10 and tension roll 11 the traveling of the single-faced corrugated board 7 is kept stable and the length of contact of the glue 9 with the board 7 is kept constant.
The single-faced corrugated board 7 fabricated by a single facer in the preceding step is entrained on a guide roll 12 and then on a preheat roll 13, whereby it is heated to a moderate extent. Thereafter, the board 7 thus heated is fed to the gluing machine 1 and comes into contact with the glue applicator roll 2 while traveling between the roll 2 and the rider roll 6, whereby the glue 9 present on the outer peripheral surface of the roll 2 is transferred and fed to the flute tips of the core board 8.
After a part of the peripheral surface of the glue applicator roll 2 is dipped in the glue reservoir 4, the amount (thickness) of glue on the outer peripheral surface of the roll 2 is controlled by the doctor roll 3 disposed adjacent the roll 2 and a long the arrowed rotational path in the figure. The surplus glue scraped off by the doctor roll 3 drops into the glue reservoir 4 and is thus recovered. The single-faced corrugated board 7 which has passed the gluing machine 1 is then fed to a heating portion 15 of a double facer 14 in the next step. In the heating portion 15, the board 7 joins a liner 16 which has been fed through another route, and both are laminated together to form a double-faced corrugated board 17.
As to the double-faced corrugated board 17, various such boards can be fabricated according to purposes of use. FIG. 8 shows an example in which two single-faced corrugated boards 7, namely a single-faced corrugated board 7a with glue 9 applied thereto by the upper glue applicator in the same figure, and a single-faced corrugated board 7b with glue 9, applied thereto by the lower glue applicator in the same figure, and the liner 16 are laminated together to form the double-faced corrugated board 17.
In each glue applicator, the rider roll 6 is disposed in an opposed relation to the glue applicator roll 2, to press the single-faced corrugated board 7 against the roll 2. The state of engagement (clearance and nipping pressure) between the glue applicator roll 2 and the rider roll 6 is an important factor which influences the quality (strength) of the double-faced corrugated board 17. For example, it is known that if the flute tips of the core board 8 are crushed, the strength of the corrugated board case using the core board 8 is deteriorated rapidly. In view of this point the rider roll 6 is supported so as to permit adjustment of its state of engagement relative to the glue applicator roll 2.
Now, with reference to FIG. 9, a description will be given of a support structure for the rider roll 6 which structure has heretofore been adopted. In the example shown in FIG. 9, the rider roll 6 is journaled at both axial ends thereof to a pair of swing brackets (arms for the rider roll) 20. The swing brackets 20 are adapted to move pivotally about a pivot shaft 18 with expansion and retraction of a cylinder 19, relative to the glue applicator roll 2, which is positioned fixedly. Eccentric rolls 21 are respectively engaged with the swing brackets 20 located at both transverse ends of the device. Vertical swing position of the swing brackets 20 can be adjusted by setting the phase angle of the eccentric rolls 21 appropriately. By so adjusting the vertical swing position of the swing brackets 20, it is possible to appropriately set the clearance between the outer peripheral surface of the rider roll 6, each journaled to a portion of the associated swing bracket 20, and the outer peripheral surface of the glue applicator roll 2.
On the other hand, as means for pressing the single-faced corrugated board 7 against the glue applicator roll 2, there has been proposed such a device as shown in FIG. 10 (described in Japanese Patent Publication No. 18386/96). According to this proposed device, a beam 22 is mounted in the axial direction of the glue applicator roll 2, a plurality of brackets 23 are attached side-by-side to the beam 22, and a plate-like shoe 25, which is adapted to move pivotally about a pin 24, is secured to the lower end of each bracket 23. A compression spring 26 is engaged with the plate-like shoe 25 on the swing end side of the shoe, while on the rear end side of the shoe 25 is provided a positioning bolt 27. The swing motion of the shoe 25 toward the glue applicator roll 2 side is restricted by the positioning bolt 27, and hence a pressing force, which permits the formation of a predetermined clearance, can be applied by the compression spring 26. The shoe 25 is arranged in a plurally divided form in the transverse direction of the single-faced corrugated board 7, so that each shoe can swing independently. Therefore, in the event of partial wear or breakage, only the part concerned need be replaced with a new one.
The single-faced corrugated board 7 is pressed against the glue applicator roll 2 by means of the rider roll 6 and the shoes 25, whereby the nipping pressure for the board 7 can be maintained at an optimum level, and hence the quality (strength) of the double-faced corrugated board 17 is kept high.
The rider roll 6 shown in FIG. 9 is for setting, in a fixed position manner, a predetermined clearance required according to the thickness of the single-faced corrugated board 7 and the type of flute. Therefore, in the case where two or more types of single-faced corrugated boards 7 differing in flutes are to be used in the same unit, it has so far been necessary to set the clearance for each type of board. Moreover, there occurs a variation in the contact pressure, due to a difference in flute tip height, which is caused by different kinds (thicknesses) of paper, or different production conditions, thus requiring a high degree of skill for clearance adjustment. Further, even in the same flute of paper, a slight difference in thickness of the single-faced corrugated board 7 can occur, according to flute handling conditions in the single facer. An initial clearance between the rider roll 6 and the glue applicator roll 2 is usually set at a value corresponding to the minimum flute height, taking variations in chevron-shaped flute height into account. With high flute tips, therefore, the amount of collapse increases, thus resulting in application of extra glue 9 to the flute tips and consequent increase in the amount of glue consumed.
In the device using the shoes 25 shown in FIG. 10, since each shoe 25 is vertically movable independently, a certain width of the single-faced corrugated board 7 permits engagement of a shoe 25 with a slight pressure width, h, at a board end, thus causing an increase of the pressing force per unit area, and consequent collapse and droop of the board end, as shown in FIG. 11(a). In the event the single-faced corrugated board 7 meanders and deviates from a shoe 25, as shown in FIG. 11(b), the leftmost end shoe 25a, in the same figure, drops lower than the surface of the board 7. Consequently, when the board 7 tries to return to the original traveling position, a side face 25b of the shifted shoe 25a, and a side end face 7c of the board 7, interfere with each other, with the likelihood of occurrence of a trouble such as flaw or damage to the side end of the board 7.
In the device using the shoes 25, moreover, since the difference in the kind (thickness) of paper or in the flute tip height causes a change in the amount of deflection of the compression spring 26, there occur variations in the pressing force applied to the shoes 25. Besides, it is impossible to change the pressing force according to flutes or according to the state (twist or corrugation) of the single-faced corrugated board 7. Further, in adjusting the pressing force for the single-faced corrugated board 7, it is necessary to stop the operation of the machine from the standpoint of safety. Since the single-faced corrugated board tends to warp, there also arises the problem that a uniform pressure is not always obtained even if the clearance alone is kept strictly in parallel. In connection with this pressing method, various improvements have so far been tried.
FIG. 12 shows an example of such pressing method, which is described in Japanese Patent Laid Open No. 78632/86. According to the illustrated method, an air pressure, which is fed through an orifice 72 from a manifold 70, and a presser shoe 71 fixed therebelow, is used to press a single-faced corrugated board against a glue applicator roll 2.
FIG. 13 shows another example, which is described in U.S. Pat. No. 4,764,236. In this example, presser shoes 75, divided in a large number, are provided longitudinally, and air is jetted from holes 76 formed therein, to press a single-faced corrugated board 7 against a glue applicator roll 2. In this case, the pressing force is buffered by means of a plate spring 77 and a coiled spring 78.
In the case where the pressing force is induced by an air pressure through the presser shoes, the clearance between the pressing shoes and the single-faced corrugated board, that is, the thickness of the air layer, is very important, and a change thereof would cause a change in the pressing force. Accordingly, a change in flute of the single-faced corrugated board, or a great change in the kind (thickness) of paper, also causes a change in the pressing force.
Since the presser shoes 75 shown in FIG. 13 are minutely divided in the transverse direction of the single-faced corrugated board, substantially the same drawbacks as in FIG. 10 are encountered. On the other hand, the presser shoe 71 shown in FIG. 12 is integral in the transverse direction, and is formed to permit a fluid jet. However, its rigid structure is disadvantageous, in that a uniform pressing force is not obtained against a non-uniform thickness in the width direction of the single-faced corrugated board.
In all of the above-described devices using a pneumatic pressure or an air film to diminish the frictional force, air is jetted from nozzles, which are directed toward the liner of the single-faced corrugated board being conveyed.
Usually in the production of corrugated boards, various widths of papers are used, ranging from the maximum width of the machine used, to about a half thereof.
Since nozzles are arranged usually over the maximum machine width, if a narrower paper is used, it follows that there is no paper at both end portions. Consequently, the air jetted from the nozzles located at both ends is directed directly to the surface of the glue applicator roll.
When air strikes against the surface of the glue applicator roll at high speed, it causes the glue to scatter, with the result that, not only the surroundings of the machine are stained, but also the glue is deposited on a paper pressing bar, etc., and becomes solidified after a long-time operation, thus making it difficult to obtain a uniform pressing force when a wider paper is then fed.